In some oil and gas drilling operations, wells may be drilled relatively close to each other. For example, Steam Assisted Gravity Drainage (SAGD) is a procedure for recovering heavy crude oil from bitumen reservoirs. Two horizontal wells are drilled into a reservoir zone wherein one well (“upper wellbore” or “injector well”) is placed a few meters above the other (“lower wellbore” or “producer well”), in the order of about 5 meters. Steam is injected into the upper wellbore to heat heavy bitumen between the two wellbores thereby causing the bitumen to drain into the lower wellbore for recovery.
The lower wellbore is typically drilled and cased first. Then, the upper wellbore has to be drilled to extend in parallel to the lower wellbore. While drilling the upper wellbore it is important to monitor the distance between the two wellbores so that upper wellbore may be steered to ensure that the distance remains constant between the two wellbores. Due to the cumulative survey error and positioning uncertainty, an inclination error of 0.1° or 0.2° could lead to a few meters of true vertical depth (TVD) error and an Azimuth error of 1° could lead to 3 to 5 meters of error at the end of the build and 10 meters at the end of the horizontal section. As a result, it is known to employ techniques such as ranging to assist in positioning the two wellbores accurately with respect to one another.
Ranging techniques include passive ranging and active ranging. In active ranging, an EM source is deployed in one wellbore and the emitted electromagnetic field is measured in the other wellbore. The distance between the two wellbores may be derived from the respective amplitudes of the transmitted electromagnetic field in one wellbore and the measured electromagnetic field in the other wellbore. U.S. Pat. No. 8,063,641 to Schlumberger Technology Corporation discloses an active ranging method which uses a pair of electromagnetic field sources in wireline equipment deployed into the lower wellbore, and an electromagnetic field sensor in a bottom hole assembly (BHA) of a drill string in the upper wellbore. The BHA includes a measurement-while-drilling (MWD) subsystem that makes measurements, process and stores information, and includes a telemetry subsystem for data and control communication with the earth's surface using known telemetry techniques, including wireless techniques like mud pulse (pressure) telemetry, EM telemetry, acoustic telemetry and wired drill pipe. The telemetry subsystem may thus transmit MWD data as well as ranging data to surface via wireless or wired drill pipe telemetry.
Operation of the electromagnetic field sensor to detect the electromagnetic fields and the MWD subsystem to take ranging surveys is controlled and synchronized from the surface. Since there is typically no direct electrical connection between the BHA and the surface, commands sent from the surface are typically transmitted wirelessly to the BHA, e.g. via an EM or other type of downlink signal. Wireless telemetry techniques face a number of techniques challenges for transmitting data between the BHA and the surface, including: increasing signal attenuation with increasing depth, decreasing data speed with increasing depth, increasing energy requirements to transmit the wireless signal with increasing depth, and signal interference caused by surface and other background noise.
While data rates tend be higher using wired drill pipe telemetry compared to wireless telemetry, the drilling operation is limited to the use of very specific drill pipe, i.e., drill pipe having a compatible network of communications wiring. Since conventional drill pipe cannot be used with wired drill pipe telemetry, using wired drill pipe to telemeter data to and from the surface reduces flexibility and potentially increases operating costs.